Recently, medical practitioners have found it useful to use robotic devices to assist in the performance of surgical procedures. A robotic device typically includes a moveable arm that comprises one or more linkages. The arm has a free, distal end that can be placed with a very high degree of accuracy. A surgical instrument designed to be applied to the surgical site is attached to the free end of the arm. The practitioner is able to precisely position the arm so as to by extrapolation, precisely position the surgical instrument at the site on the patient at which the instrument is to perform a medical or surgical procedure. One advantage of using a robotic system to hold the instrument is that the system arm, unlike the arms and hands of a surgeon, are not subjected to muscle strain or neurological actions like twitching. Thus, in comparison to when an instrument is hand held and therefore hand positioned, using a medical robotic system it is possible to hold an instrument steady, or move the instrument along a defined path with a higher degree of accuracy.
Further some robotic surgical systems are designed to be used with surgical navigation systems. A surgical navigation system is a system that is able to generate data that provides a relatively precise indication of the surgical instrument relative to the location of the patient against which the instrument is applied. When a surgical robotic system is provided with the data indicating the position of the instrument relative to the patient, the robotic system may be able to position the instrument to ensure that it is applied to the tissue of the patient against which the instrument is supposed to be applied. This substantially eliminates the likelihood that the instrument will be applied to tissue against which the instrument should not be applied.
Some medical robotic systems are designed to work in what is referred to as a “semi-autonomous” mode. In this mode of operation, the robotic system actuates the arm so as to cause the instrument to move against the patient's tissue in a preprogrammed path. This is useful if, for example, the instrument is some sort of cutting device and the goal of the particular procedure is to remove a pre-defined section of the patient's tissue. By way of reference, if a robotic system operates in an “autonomous” mode of operation, the robot, once actuated, performs the procedure with essentially no input from the surgeon. In a “semi-autonomous” mode of operation, the practitioner is able to assert commands to control the operation of the robot. For example, some semi-autonomous robots are constructed so that, in order for the robot to displace the instrument, the practitioner must actuate a command by continually depressing a control button or switch associated with the robot. Upon the negation of the actuate command by the practitioner, the advancement of the instrument by the robot at least temporarily stops.
Some robotic systems are not traditional robots in that once activated, they do not automatically move the attached instrument along a pre-programmed path of travel. These systems include control systems through which the practitioner enters commands indicating where the attached instrument is to be positioned. Based on these practitioner-entered commands, this type of system actuates the system's arm/arms to cause the essentially simultaneous, real time, movement of the instrument. These robotics systems are considered to operate in a manual mode.
To date though, it has been difficult to provide a robotic system able to, during the performance of a single procedure, switch between semi-autonomous and manual modes of operation. For example, it is believed that many times a surgeon may want to initially manually operate the instrument in order to remove a large mass of tissue. This part of the procedure is sometimes referred to as debulking. Then, to remove tissue to define the surfaces of the remaining tissue, the surgeon may want the robotic system to semi-autonomously perform fine positioning of the instrument. This part of the procedure is sometimes known as the finishing cut.
Moreover, there are times when it may be desirable to switch from semi-autonomous positioning of the instrument back to manual positioning. For example, in an orthopedic joint replacement procedure, the practitioner may want the instrument, a cutting tool, to move in a programmed path in order to precisely shape the bone to which the instrument is applied. This precise bone shaping facilitates the precise fitting of the implant to the face of the bone exposed by the cutting tool. However, there may be a situation in which, after the procedure begins, it becomes apparent that the instrument may collide with an object at the surgical site against which such contact is undesirable. This object may be tissue that has moved into the surgical site or a second instrument positioned at the site. In this situation, it should be possible for the practitioner to momentarily interrupt the programmed movement of the tool, manually control the tool to reposition the instrument, and then return the tool to the programmed movement.